An improved spectroscopy is used to implement and optimize the retrieval strategy of ethane (C2H6) from ground-based Fourier Transform Infrared (FTIR) solar spectra recorded at the high-altitude station ... [more ▼]

An improved spectroscopy is used to implement and optimize the retrieval strategy of ethane (C2H6) from ground-based Fourier Transform Infrared (FTIR) solar spectra recorded at the high-altitude station of Jungfraujoch (Swiss Alps, 46.5° N, 8.0° E, 3580m a.s.l.). The improved spectroscopic parameters include C2H6 pseudo-lines in the 2720-3100 cm-1 range and updated line parameters for methyl chloride and ozone. These improved spectroscopic parameters allow for substantial reduction of the fitting residuals as well as enhanced information content. They also contribute to limiting oscillations responsible for ungeophysical negative mixing ratio profiles. This strategy has been successfully applied to the Jungfraujoch solar spectra available from 1994 onwards. The resulting time series is compared with C2H6 total columns simulated by the state-of-the-art chemical transport model GEOS-Chem. Despite very consistent seasonal cycles between both data sets, a negative systematic bias relative to the FTIR observations suggests that C2H6 emissions are underestimated in the current inventories implemented in GEOS-Chem. Finally, C2H6 trends are derived from the FTIR time series, revealing a statistically-significant sharp increase of the C2H6 burden in the remote atmosphere above Jungfraujoch since 2009. Evaluating cause of this change in the C2H6 burden, which may be related to the recent massive growth of shale gas exploitation in North America, is of primary importance for atmospheric composition and air quality in the Northern Hemisphere. [less ▲]

Methanol (CH3OH) is the second most abundant organic compound in the Earth's atmosphere after methane. In this work, we present the first long-term time series of methanol total, lower tropospheric and ... [more ▼]

Methanol (CH3OH) is the second most abundant organic compound in the Earth's atmosphere after methane. In this work, we present the first long-term time series of methanol total, lower tropospheric and upper tropospheric-lower stratospheric partial columns derived from the analysis of high resolution Fourier transform infrared solar spectra recorded at the Jungfraujoch station (46.5° N, 3580 m a.s.l.). The retrieval of methanol is very challenging due to strong absorptions of ozone in the region of the selected υ8 band of CH3OH. Two wide spectral intervals have been defined and adjusted in order to maximize the information content. Methanol does not exhibit a significant trend over the 1995–2012 time period, but a strong seasonal modulation characterized by maximum values and variability in June–July, minimum columns in winter and a peak-to-peak amplitude of 130%. In situ measurements performed at the Jungfraujoch and ACE-FTS occultations give similar results for the methanol seasonal variation. The total and lower tropospheric columns are also compared with IMAGESv2 model simulations. There is no systematic bias between the observations and IMAGESv2 but the model underestimates the peak-to-peak amplitude of the seasonal modulations. [less ▲]

As a ubiquitous product of the oxidation of many Volatile Organic Compounds (VOCs), formaldehyde (HCHO) plays a key role as a short-lived and reactive intermediate in the atmospheric photo-oxidation ... [more ▼]

As a ubiquitous product of the oxidation of many Volatile Organic Compounds (VOCs), formaldehyde (HCHO) plays a key role as a short-lived and reactive intermediate in the atmospheric photo-oxidation pathways leading to the formation of tropospheric ozone and secondary organic aerosols. We have successfully retrieved HCHO columns from ground-based Fourier Transform Infrared (FTIR) solar spectra and UV-Visible Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) scans recorded during the July 2010 – December 2012 time period at the Jungfraujoch station (Swiss Alps, 46.5 °N, 8.0 °E, 3580 m a.s.l.). Characterization of the retrieved products has revealed different vertical sensitivity between both remote sensing techniques. Furthermore, HCHO amounts simulated by two state-of-the-art Chemical Transport Models (CTMs), GEOS-Chem and IMAGESv2, have been compared to FTIR total columns and MAX-DOAS 3.6 – 8 km partial columns, accounting for the respective vertical resolution of each ground-based instrument. Using the CTMs outputs as intermediate, FTIR and MAX-DOAS retrievals have shown consistent seasonal modulations of HCHO throughout the investigated period, characterized by summertime maximum and wintertime minimum. Such comparisons have also highlighted that FTIR and MAX-DOAS provide complementary products for HCHO above the Jungfraujoch station. [less ▲]

The abundance of chlorine in the Earth’s atmosphere increased considerably during the 1970s to 1990s, following large emissions of anthropogenic long-lived chlorine-containing source gases, notably the ... [more ▼]

The abundance of chlorine in the Earth’s atmosphere increased considerably during the 1970s to 1990s, following large emissions of anthropogenic long-lived chlorine-containing source gases, notably the chlorofluorocarbons. The chemical inertness of chlorofluorocarbons allows their transport and mixing throughout the troposphere on a global scale[1], before they reach the stratosphere where they release chlorine atoms that cause ozone depletion[2]. The large ozone loss over Antarctica[3] was the key observation that stimulated the definition and signing in 1987 of the Montreal Protocol, an international treaty establishing a schedule to reduce the production of the major chlorine- and bromine-containing halocarbons. Owing to its implementation, the near-surface total chlorine concentration showed a maximum in 1993, followed by a decrease of half a per cent to one per cent per year[4], in line with expectations. Remote-sensing data have revealed a peak in stratospheric chlorine after 1996[5], then a decrease of close to one per cent per year[6,7], in agreement with the surface observations of the chlorine source gases and model calculations[7]. Here we present ground-based and satellite data that show a recent and significant increase, at the 2σ level, in hydrogen chloride (HCl), the main stratospheric chlorine reservoir, starting around 2007 in the lower stratosphere of the Northern Hemisphere, in contrast with the ongoing monotonic decrease of near-surface source gases. Using model simulations, we attribute this trend anomaly to a slowdown in the Northern Hemisphere atmospheric circulation, occurring over several consecutive years, transporting more aged air to the lower stratosphere, and characterized by a larger relative conversion of source gases to HCl. This short-term dynamical variability will also affect other stratospheric tracers and needs to be accounted for when studying the evolution of the stratospheric ozone layer. [less ▲]

in Atmospheric Measurement Techniques. Papers in Open Discussion (2014), 7

As a ubiquitous product of the oxidation of many Volatile Organic Compounds (VOCs), formaldehyde (HCHO) plays a key role as a short-lived and reactive intermediate in the atmospheric photo-oxidation ... [more ▼]

As a ubiquitous product of the oxidation of many Volatile Organic Compounds (VOCs), formaldehyde (HCHO) plays a key role as a short-lived and reactive intermediate in the atmospheric photo-oxidation pathways leading to the formation of tropospheric ozone and secondary organic aerosols. In this study, HCHO profiles have been successfully retrieved from ground-based Fourier Transform Infrared (FTIR) solar spectra and UV-Visible Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) scans recorded during the July 2010–December 2012 time period at the Jungfraujoch station (Swiss Alps, 46.5 N, 8.0 E, 3580ma.s.l.). Analysis of the retrieved products has revealed different vertical sensitivity between both remote sensing techniques. Furthermore, HCHO amounts simulated by two state-of-the-art Chemical Transport Models (CTMs), GEOS-Chem and IMAGESv2, have been compared to FTIR total columns and MAX-DOAS 3.6–8 km partial columns, accounting for the respective vertical resolution of each ground-based instrument. Using the CTMs outputs as intermediate, FTIR and MAX-DOAS retrievals have shown consistent seasonal modulations of HCHO throughout the investigated period, characterized by summertime maximum and wintertime minimum. Such comparisons have also highlighted that FTIR and MAX-DOAS provide complementary products for the HCHO retrieval above the Jungfraujoch station. [less ▲]

Relying on high-resolution Fourier transform infrared (FTIR) spectra, the present work involved extensive measurements of individual line intensities and self-broadening coefficients for the ν7 band of ... [more ▼]

Relying on high-resolution Fourier transform infrared (FTIR) spectra, the present work involved extensive measurements of individual line intensities and self-broadening coefficients for the ν7 band of 12C2H4. The measured self-broadening coefficients exhibit a dependence on both J and Ka. Compared to the corresponding information available in the latest edition of the HITRAN spectroscopic database, the measured line intensities were found to be higher by about 10 % for high J lines in the P branch and lower by about 5 % for high J lines of the R branch, varying between these two limits roughly linearly with the line positions. The impact of the presently measured line intensities on retrievals of atmospheric ethylene in the 949.0–952.0cm 1 microwindow was evaluated using a subset of ground-based high-resolution FTIR solar spectra recorded at the Jungfraujoch station. The use of HITRAN 2012 with line intensities modified to match the present measurements led to a systematic reduction of the measured total columns of ethylene by -4.1 +/- 0.1 %. [less ▲]

Relying on high-resolution Fourier transform infrared (FTIR) spectra, the present work involved extensive measurements of individual line intensities and self broadening coefficients for the nu7 band of ... [more ▼]

Relying on high-resolution Fourier transform infrared (FTIR) spectra, the present work involved extensive measurements of individual line intensities and self broadening coefficients for the nu7 band of 12C2H4. The measured self broadening coefficients exhibit a dependence on both J and Ka. Compared to the corresponding information available in the latest edition of the HITRAN spectroscopic database, the measured line intensities were found to be higher by about 10 % for high J lines in the P branch and lower by about 5 % for high J lines of the R branch, varying between these two limits roughly linearly with the line positions. The impact of the presently measured line intensities on retrievals of atmospheric ethylene in the 949.0-952.0 cm-1 microwindow was evaluated using a subset of ground-based high-resolution FTIR solar spectra recorded at the Jungfraujoch station. The use of HITRAN 2012 with line intensities modified to match the present measurements led to a systematic reduction of the measured total columns of ethylene by -4.1+/-0.1 %. [less ▲]

Ethylene (ethene, C2H4) is a tropospheric pollutant on the Earth, also present as a by-product of methane photochemistry in the atmosphere of outer solar system bodies. Remote sensing of ethylene in the ... [more ▼]

Ethylene (ethene, C2H4) is a tropospheric pollutant on the Earth, also present as a by-product of methane photochemistry in the atmosphere of outer solar system bodies. Remote sensing of ethylene in the infrared range relies on the 10 mm region. This spectral range corresponds to the excitation of 7 modes of vibration of 12C2H4, 4 of which being infrared active (see Fig. 1 of [1]). The corresponding n10, n7, n4 and n12 bands are located near 826, 949, 1026 and 1442 cm-1, respectively [1]. Among these, the n7 band is the strongest, indeed used for remote sensing measurements of ethylene. Relying on high-resolution Fourier transform infrared (FTIR) spectra recorded in Brussels, the present work involved extensive measurements of individual line intensities and self broadening coefficients for the n7 band of 12C2H4. Compared to the corresponding information available in the latest edition of the HITRAN spectroscopic database (HITRAN 2012 [2]), the measured line intensities were found to be higher by about 10 % for high J lines in the P branch and lower by about 5 % for high J lines of the R branch, varying between these two limits roughly linearly with the line positions. Test calculations performed in this work indicated that these discrepancies could result from the relative values of the transition moments of the n10, n7 and n12 bands used when the information provided in HITRAN was generated (the transition moment of the n4 band was set to zero). The measured self broadening coefficients exhibit a dependence on both J and Ka, which was modeled empirically. The spectroscopic information for ethylene available in HITRAN 2012 was modified to match the present observations. The impact of these modifications on retrievals of atmospheric ethylene was then evaluated via FTIR retrievals in the 949.0 – 952.0 cm-1 microwindow, from a subset of ground-based high-resolution FTIR solar spectra recorded at the Jungfraujoch station. The new line intensities were found to lead to a reduction of the measured total columns of ethylene by -4.1±0.1 %, compared to the use of HITRAN 2012. [less ▲]

Methanol (CH3OH) is the second most abundant organic compound in the Earth’s atmosphere after methane. In this work, we present the first long-term time series of methanol total, lower tropospheric and ... [more ▼]

Methanol (CH3OH) is the second most abundant organic compound in the Earth’s atmosphere after methane. In this work, we present the first long-term time series of methanol total, lower tropospheric and upper tropospheric-lower stratospheric partial columns derived from the analysis of high resolution Fourier transform infrared solar spectra recorded at the Jungfraujoch station (46.5°N, 3580 m a.s.l.). The retrieval of methanol is very challenging due to strong absorptions of ozone in the region of the selected 8 band of CH3OH. Two wide spectral intervals have been defined and adjusted in order to maximize the information content. Methanol does not exhibit a significant trend over the 1995-2012 time period, but a strong seasonal modulation characterized by maximum values and variability in June-July, minimum columns in winter and a peak-to-peak amplitude of 130 %. In situ measurements performed at the Jungfraujoch and ACE-FTS occultations give similar results for the methanol seasonal variation. The total and lower tropospheric columns are also compared with IMAGESv2 model simulations. There is no systematic bias between the observations and IMAGESv2 but the model underestimates the peak-to-peak amplitude of the seasonal modulations. [less ▲]

Formaldehyde (HCHO) plays an important intermediate role in the atmospheric photo-oxidation pathways. It is produced during the oxidation of methane and many non-methane volatile organic compounds (NMVOCs ... [more ▼]

Formaldehyde (HCHO) plays an important intermediate role in the atmospheric photo-oxidation pathways. It is produced during the oxidation of methane and many non-methane volatile organic compounds (NMVOCs) which participate to the formation of tropospheric ozone and secondary organic aerosols. HCHO is also directly released by biomass burning and fossil fuel combustion and to a lesser extent by vegetation. Measuring this species is therefore of major importance for air quality and climate change monitoring. In this presentation, HCHO near-surface concentrations and vertical column densities are retrieved from MAX-DOAS measurements performed at the high-altitude station of Jungfraujoch (3580m asl) in the Swiss Alps from July 2010 till December 2012. Although being most of the time located in the free troposphere, this station can be temporarily affected by pollution events originating from the valley, leading to a local increase of air pollutant concentrations. The capability of the MAX-DOAS technique to retrieve HCHO in such high-altitude location is investigated. The spatial representativeness and the impact of cloud cover on the measurements is also discussed. For verification purpose, our retrievals are compared to collocated FTIR observations, taking into account the difference in vertical resolution between both techniques. Simulations from the 3D-CTM IMAGES are also used to further assess the observed seasonal and diurnal cycles of HCHO surface concentration and vertical column. [less ▲]

In the framework of the NORS project, a retrieval strategy for formaldehyde (H2CO) is currently under development, using measurements from ground-based high-resolution FTIR solar spectra recorded at the ... [more ▼]

In the framework of the NORS project, a retrieval strategy for formaldehyde (H2CO) is currently under development, using measurements from ground-based high-resolution FTIR solar spectra recorded at the NDACC high altitude station of the Jungfraujoch (Swiss Alps, 46.5° N, 8.0° E, 3580m a.s.l.). According to the preliminary results, our FTIR retrieval strategy based on Tikhonov regularization has proven able to make an improvement in the process of fitting the H2CO feature within the 2833.070 – 2833.350 cm-1 microwindow from Jungfraujoch solar spectra, compared to a simple scaling. Furthermore, the retrieved total columns present a seasonal cycle averaged over 2005 – 2013 in agreement with preliminary results from UV-visible MAX-DOAS observations, ACE-FTS occultation measurements and simulations from the IMAGES and GEOS-CHEM models. However, FTIR H2CO abundances appear to be underestimated during summertime, with respect to the other data sets. In order to solve this issue, further experiments are planned. [less ▲]

We present an overview of the geophysical data deduced from long-term monitoring activities conducted at the Jungfraujoch station by the University of Liège. Typical results and trend investigations are ... [more ▼]

We present an overview of the geophysical data deduced from long-term monitoring activities conducted at the Jungfraujoch station by the University of Liège. Typical results and trend investigations are presented for hydrogen chloride (HCl) and carbonyl sulfide (OCS). We further display and briefly describe time series for new target gases, namely methanol (CH3OH) and HCFC-142b. We also show some preliminary results for ammonia (NH3) and peroxyacetyl nitrate (PAN). Finally, we present the PyGChem project, a Python interface to the GEOS-Chem model currently under development at ULg. [less ▲]

To estimate the sea level rise (SLR) originating from changes in surface mass balance (SMB) of the Greenland ice sheet (GrIS), we present 21st century climate projections obtained with the regional climate model MAR (Modèle Atmosphérique Régional), forced by output of three CMIP5 (Coupled Model Intercomparison Project Phase 5) general circulation models (GCMs). Our results indicate that in a warmer climate, mass gain from increased winter snowfall over the GrIS does not compensate mass loss through increased meltwater run-off in summer. Despite the large spread in the projected near-surface warming, all the MAR projections show similar non-linear increase of GrIS surface melt volume because no change is projected in the general atmospheric circulation over Greenland. By coarsely estimating the GrIS SMB changes from GCM output, we show that the uncertainty from the GCM-based forcing represents about half of the projected SMB changes. In 2100, the CMIP5 ensemble mean projects a GrIS SMB decrease equivalent to a mean SLR of +4 ± 2 cm and +9 ± 4 cm for the RCP (Representative Concentration Pathways) 4.5 and RCP 8.5 scenarios respectively. These estimates do not consider the positive melt–elevation feedback, although sensitivity experiments using perturbed ice sheet topographies consistent with the projected SMB changes demonstrate that this is a significant feedback, and highlight the importance of coupling regional climate models to an ice sheet model. Such a coupling will allow the assessment of future response of both surface processes and ice-dynamic changes to rising temperatures, as well as their mutual feedbacks. [less ▲]

In this study, simulations at 25 km resolution are performed over the Greenland ice sheet (GrIS) throughout the 20th and 21st centuries, using the regional climate model MAR forced by four RCP scenarios ... [more ▼]

In this study, simulations at 25 km resolution are performed over the Greenland ice sheet (GrIS) throughout the 20th and 21st centuries, using the regional climate model MAR forced by four RCP scenarios from three CMIP5 global circulation models (GCMs), in order to investigate the projected changes of the surface energy balance (SEB) components driving the surface melt. Analysis of 2000–2100 melt anomalies compared to melt results over 1980–1999 reveals an exponential relationship of the GrIS surface melt rate simulated by MAR to the near-surface air temperature (TAS) anomalies, mainly due to the surface albedo positive feedback associated with the extension of bare ice areas in summer. On the GrIS margins, the future melt anomalies are preferentially driven by stronger sensible heat fluxes, induced by enhanced warm air advection over the ice sheet. Over the central dry snow zone, the surface albedo positive feedback induced by the increase in summer melt exceeds the negative feedback of heavier snowfall for TAS anomalies higher than 4 °C. In addition to the incoming longwave flux increase associated with the atmosphere warming, GCM-forced MAR simulations project an increase of the cloud cover decreasing the ratio of the incoming shortwave versus longwave radiation and dampening the albedo feedback. However, it should be noted that this trend in the cloud cover is contrary to that simulated by ERA-Interim–forced MAR for recent climate conditions, where the observed melt increase since the 1990s seems mainly to be a consequence of more anticyclonic atmospheric conditions. Finally, no significant change is projected in the length of the melt season, which highlights the importance of solar radiation absorbed by the ice sheet surface in the melt SEB. [less ▲]

The Greenland ice sheet (GrIS) surface mass balance (SMB) was modelled at different spatial resolutions (15-50 km), using the regional climate model MAR (Modèle Atmosphérique Régional) forced by the ERA-INTERIM reanalysis over the 1990-2010 period. The comparison of these simulations revealed that (i) the inter-annual variability of the SMB components is consistent within the different resolutions investigated when they are integrated over the whole ice sheet, (ii) the MAR model simulates heavier precipitation on average over the GrIS with decreasing resolution, and (iii) the SMB components (except precipitation) can be derived from a lower-resolution simulation with an enhanced interpolation. This interpolation can also be used to approximate the SMB components over another topography/ice sheet mask of the GrIS. These results are valuable for the forcing of an ice dynamical model, needed to enable full projections of the GrIS mass balance contribution to sea-level rise (SLR) over the coming centuries. Moreover, this work showed that 25 km-resolution MAR simulation is a good compromise between computing time and results precision in the aim to perform afterwards 21st-century projections of the GrIS melt. The most suited atmosphere-ocean general circulation models (AOGCMs) for the GrIS current climate modelling were selected on the basis of comparison between the 1970-1999 outputs and reanalyses, showing that the representation quality of surface parameters (temperature, precipitation) are highly correlated to the atmospheric circulation and its inter-annual variability (North Atlantic oscillation). Future atmospheric circulation changes according to greenhouse gas (GHG) emissions scenarios were projected to dampen the zonal flow, enhance the meridional fluxes and provide additional heat and moisture to the GrIS, increasing temperature over the whole ice sheet and precipitation over its northeastern area. Moreover, future projections performed with the selected AOGCMs showed consistent anomalies to the present-day climate. The GrIS SMB anomalies from the A1B scenario amount to -300 Gt/yr with respect to 1970-1999, leading to a SLR of 5 cm by the end of the 21st century. This work helped to select the AOGCMs used as forcing fields in the MAR model to carry out future projections of the GrIS. 20th and 21st centuries MAR simulations at 25km resolution forced by previously selected GCMs according to GHG scenarios were performed over the GrIS in order to investigate the projected changes of the surface energy balance (SEB) components driving the surface melt. Analysis of 2000-2100 melt anomalies to 1980–1999 results revealed an exponential relationship of the surface melt to the near-surface temperature anomalies, mainly due to the surface albedo positive feedback associated with the extension of bare ice areas in summer. On the GrIS margins, the future melt anomalies are driven by stronger sensible heat fluxes, induced by enhanced warm air advections. Over the central dry snow zone, the increase of melt surpasses the negative feedback from heavier snowfall inducing a decrease of the summer surface albedo. In addition to the incoming longwave flux increase associated to the atmosphere warming, MAR projected an increase of the cloud cover decreasing the ratio of the incoming shortwave versus longwave radiation and dampening the albedo feedback. This trend of cloud cover is contrary to that simulated by reanalyses-forced MAR over current climate, where the observed melt increase since the 1990’s is rather a consequence of more anticyclonic atmospheric conditions. No significant change was projected in the length of the melt season, highlighting the importance of solar radiation in the melt SEB. [less ▲]

As part of the ICE2SEA project, the regional climate model MAR was forced by the global models HadCM3 and ECHAM5 for making future projections of the Greenland Ice Sheet (GrIS) Surface Mass Balance (SMB ... [more ▼]

As part of the ICE2SEA project, the regional climate model MAR was forced by the global models HadCM3 and ECHAM5 for making future projections of the Greenland Ice Sheet (GrIS) Surface Mass Balance (SMB) over 1980-2099 at a resolution of 25km. However, the comparison with MAR forced by the ERA-40 reanalysis over 1980-1999 shows that MAR forced by these GCMs is not able to represent reliably the current SMB due to biases in the general circulation and in the free atmosphere summer temperature modelled by these GCMs around the GrIS. That is why, we present here first results of MAR forced by the next generation of GCMs from the CMIP5 data base (CanESM2, NorESM1 and MIROC5 here). The comparison with the ERA-INTERIM forced MAR simulations over current climate is a lot of better, which increases the reliability and the interest of these new MAR projections. In addition, the new scenarios (RCP 2.6, 4.5, 6.0 and 8.5) of the next IPCC Assessment Report (AR5) are used here. These new simulations show notably that the response of SMB to rising temperature is not a linear function of the temperature anomalies due to the positive albedo feedback which enhances the surface melt. For 2100, in case of extreme rising temperature (RCP 8.5 scenario), MAR simulates a surface GrIS mass loss corresponding to a cumulated sea level rise (SLR) of about 15 cm since 2000! Mainly the changes in SMB and in surface energy balance will be discussed here and estimations of the GrIS surface melt contribution to the SLR using all the CMIP5 outputs will be given. [less ▲]

With the aim to force an ice dynamical model, the Greenland ice sheet (GrIS) surface mass balance (SMB) was modelled at different spatial resolutions (15-50 km) for the period 1990-2010, using the ... [more ▼]

With the aim to force an ice dynamical model, the Greenland ice sheet (GrIS) surface mass balance (SMB) was modelled at different spatial resolutions (15-50 km) for the period 1990-2010, using the regional climate model MAR (Modèle Atmosphérique Régional) forced by the ERA-INTERIM reanalysis. This comparison revealed that (i) the inter-annual variability of the SMB components is consistent within the different spatial resolutions investigated, (ii) the MAR model simulates heavier precipitation on average over the GrIS with diminishing spatial resolution, and (iii) the SMB components (except precipitation) can be derived from a simulation at lower resolution with an intelligent interpolation. This interpolation can also be used to approximate the SMB components over another topography/ice sheet mask of the GrIS. These results are important for the forcing of an ice dynamical model, needed to enable future projections of the GrIS contribution to sea level rise over the coming centuries. [less ▲]